Non-line-of-sight, NLOS, communication refers to wireless communication between a transmitter and at least one receiver where a transmitted signal propagates along at least one in-direct path between the transmitter and the at least one receiver. Such in-direct propagation paths can for example arise due to reflection and/or diffraction effects in the surrounding environment. It should be noted that, due to the above definition, NLOS communication herein comprises also communication wherein a line-of-sight, LOS, component exists in addition to the one or several NLOS propagation paths.
A directive radio antenna is an antenna which is configured to focus emitted electromagnetical energy in a pre-determined direction, i.e., in a given elevation angle and azimuth angle, thus providing an increased antenna gain in that pre-determined direction compared to other transmit directions. Herein, this focus of energy will be referred to as the antenna main lobe. Due to reciprocity, the direction of maximum transmit gain often co-incides with the direction of maximum receive gain, i.e., the elevation angle and azimuth angle of the transmit and receive antenna main lobes often co-incide. Thus, herein, no distinction will be made between transmit and receive antenna main lobes. It is however understood that transmit and receive antenna main lobes can differ both in width as well as azimuth angle and elevation angle.
In order to reach full potential in the communication capacity of a communication system utilizing one or several directive antennas, the directive antenna or antennas must be carefully positioned and the antenna main lobes directed with respect to each other in order to optimize the performance of the communication system in terms of, e.g., received signal power and bit-error-rate, BER.
A directive radio antenna when properly positioned and directed often provides superior communication system performance as compared to an isotropic antenna which radiates an equal amount of energy in all directions. However, a flawed positioning or directing may have dire consequences in terms of received signal power and BER. Thus, positioning and directing of radio antennas are crucial when, e.g., deploying a radio link such as a microwave radio link.
The directing of antenna main lobes in azimuth angle and elevation angle is often referred to as aligning of the radio antennas, even if said directing is not performed with respect to a line of sight, LOS, between antennas. Thus, herein, aligning of radio antennas refers to the directing of one or several antenna main lobes with respect to one or several inbound radio signals, and not necessarily to directing with respect to a physical location or direction of another antenna.
Positioning and aligning directive antennas, and especially antennas with narrow antenna main lobes, can be time consuming and thus costly. The reason being that propagation phenomena such as reflection, diffraction, and penetration may give rise to complicated received fields of electromagnetical energy, where, e.g., received signal power as a function of antenna main lobe direction is not a unimodal function of position and antenna main lobe direction. Hence there is a need for improvements in antenna aligning procedure to reduce antenna deployment time and cost.
Positioning and aligning directive antennas in NLOS communication systems can be especially challenging, due to that a plurality of propagation paths between transmitter and receiver exist. This is especially true in urban environments where finding a suitable NLOS propagation path often requires both positioning and directing of antennas. Hence there is a need for an antenna alignment procedure which allows efficient and accurate positioning and directing of antennas in NLOS communication environments.